'Dozens dead' after explosions rip through Belgium's capital
This includes 20 dead in a blast at a metro station in Brussels.
Soldiers are patrolling Brussels' streets after two bombs went off at the city's international airport and another at Maalbeck metro station close to the European Union headquarters.
Vigils are being held across the city and messages of solidarity shared on social media with the victims of the attacks.
Belgium authorities have warned the public that the attackers could still be at large.
Meanwhile, Tihange nuclear power station in Liege has been evacuated, Belgium media reported however this was later denied by the operators.
Elswhere, passengers have been told to stay on trains until escorted to safety by police.
Other Brussels' residents have been asked to remain in their homes or offices, and urged to leave their children in schools as the manhunt for the killers continues and rescue efforts continue.
The attacks coincided with Brussels peak hour for commuters when trains and buses were packed. At least one explosion close to the European Union headquarters, in the city centre.
The other bombings took place at the capital's busy international airport during another rush hour period.
It is clear that the assailants wanted to inflict maximum casualties in the attacks.
The city is particularly symbolic as Brussels houses the European Union headquarters and widely viewed as the heart of modern Europe, politicians across the continent have said.
Leaders across the EU have made statements and speeches of sympathy and solidarity. Others have responded in hurt and anger.
France's Prime Minister Manuel Valis described the attacks as "acts of war", while Paris offered medical aid to its northern neighbour.
All trams, trains and buse services in the Belgium capital have been cancelled. Passengers on trains are being evacuated by police along quiet train tracks.
Students and school children have been told to wait in their classrooms while Belgium's terror threat remains at its highest levels.
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Hospitals have called for urgent blood donations while medics and doctors attempt to cope with scores of injured patients coming in.
Belgians have also been asked to car-pool as thousands of people remain trapped in the centre with public transport down and phone lines jammed.
Authorities called on Belgians to keep the internet free for communication and avoid streaming videos.
It comes after the twin blasts at Brussels Zaventem airport, with reports of gunfire accompanying the explosions.
Police said they found a AK-47 assault rifle on one of the suspects killed in the attack. Police said that at least one of the explosions was the result of a suicide bomber.
Another explosion ripped through the packed Maalbeck metro station, close to the European Union headquarters.
Firefighters working at the site said at least 15 people died in the attack.
Dozens more were injured, many seriously, they said.
Addressing the nation
Belgium's Prime Minister Charles Michel updated the nation on the situation.
He warned there are "scores dead and scores injured", some seriously.
Military reinforcements and border controls have been stepped up. Despite the chaos in the capital, Charles called for calm.
"In this black moment for this country I would like everyone to show calmness… we should face up to this challenge to be united, show solidarity and stand together in this challenging time."
Around 250 troops were deployed to Brussels to cope with the situation.
Authorities closed metro, train, tram and bus services fearing further attacks.
"Bus, tram and metro shut down," the Brussels public transport operator STIB said in a message on Twitter. Major railway stations are also closed, the Brussels public prosecutor said.
Nuclear plants in Belgium are also seeing an increase in guarding and surveillance.
Belgium authorities have formally confirmed that the three bombings were the result of "terror attacks".
Other European countries have responded to the threat with a further 1,600 police sent to the French border with Belgium. The Netherlands has tightened security on its border.
Paris and London airports have also seen security stepped up, while the UK-London Eurostar rail service to Brussels has been suspended.
UK Prime Minister David Cameron will hold a COBRA committee meeting with military and intelligence chiefs to discuss the domestic threat of terrorism.
Belgian officials scambled to evacuate the airport and assess the situation following the bombing.
Witnesses said that the second explosion happened in an area of the airport where people had gathered after fleeing the first bomb.
In the confusion, reports of other explosions were reported. Bomb squads remain on location and are thought to be carrying out controlled explosions of suspect packages.
Witnesses who have taken to social media in the immediate aftermath of the 8:00am explosions describe hearing bursts of gunfire shortly before the blasts.
The explosions come after a week of intense counter-terrorism efforts across Belgium, particularly in the capital, as Salah Abdelsalam - a fugitive suspected of involvement in November's Paris attacks - was shot and arrested by police on Friday.
Abdelsalam is thought to have fled the scene of the Paris attacks, after dropping off other militants in a rental car before the attacks commenced. He was then reportedly driven to Brussels, passing at least three police checkpoints on the way.
An assault rifle, a book about Salafism and the black flag of the Islamic State group were reportedly found during a raid on a Brussels apartment in which he'd been staying.
David Cameron, Britain's prime minister published a brief statement on Tuesday morning, saying: "I am shocked and concerned by the events. We will do everything we can to help."
Metro train stations across the Belgian capital were evacuated and shuttered, as reports emerged of a third explosion outside EU officials' offices.
Although unconfirmed reports on social media said there had been "shouting in Arabic" moments before Tuesday morning's twin explosions, there has been no official confirmation of any attackers' motivations.